1. Field of the Invention
The present invention relates to a unit and method for performing a Discrete Wavelet Transform (DWT) and an Inverse Discrete Wavelet Transform (IDWT) in a Joint Photographic Experts Group standard (JPEG) 2000, and more particularly to a unit and method for performing the DWT and IDWT in the JPEG 2000 capable of adaptively encoding/decoding the DWT and IDWT based on the energy of each inputted image block at each time-domain in a coder/decoder (CODEC) of the JPEG 2000 in a proper manner.
2. Description of the Related Art
The JPEG standard, an international compression standard for continuous-tone still images, has been selected as a still image compression standard and has greatly served multimedia services through provision of a variety of computer applications and hardwires. However, the JPEG standard is restricted to its applicable field due to its limited performance. To be more specific, the limited performance of the JPEG standard is exemplified by a low compression capability, an un-integrated lossy/lossless compression system, a non-applicability of high capacity images, a low transmission stability under a noisy environment, a compression degradation of synthetic images such as graphics, compression deterioration of a compound document and so forth.
To overcome these problems of the JPEG standard, a JPEG 2000 standard has been proposed. The JPEG 2000 standard is a standard for the next generation of still images, which incorporates various functions into the JPEG standard. Particularly, a standardization of the JPEG 2000 standard is conducted by International Telecommunication Union Sub Group 8 (ITU-R SG8) and International Organization For Standardization/International Electronical Commission Joint Technical Committee 1/Sub Committee 29/Working Group 1 (ISO/IEC JTC1/SC29/WG1) at the same time. The JPEG 2000 standard endows one integrated code to various types of still images, which have different characteristics from each other, such as natural images, scientific images, medical images, remote sensing images, document images, graphic images and so on.
The JPEG 2000 standard can be variously used throughout all the fields associated with the still images, for example medical images, the Internet/WWW images, remote sensing, image archiving, graphics and computer synthetic images, facsimiles, printing and publishing images, laser images, digital camera, scanner and digital photocopier, economical documents, security camera, earth imaging, digital library for photographs and arts, camera phones and so on.
Recently, there emerged gradually increasing requirements to transmit an immense quantity of data at a very high speed in the environment of low transmission rate and narrow bandwidth, such as on a computer network, a public telephone network, a radio channel or the like, for communication of various multi-media.
Independently encoded/decoded moving pictures based on the Moving Picture Expert Group (MPEG) or the image codec H.26× or still images according to the JPEG standard, various techniques such as a Discrete Cosine Transform (DCT), (Discrete Wavelet Transform (DWT), Motion Estimation (ME) and Motion Compensation (MC) are used to perform data compression transformation based on a block of images, which are separated by a desired size. When data is transmitted using this data compression transformation, a transmission rate of data is low, and a minimum image quality, which a user considers to be satisfactory is not ensured.
According to technical advancements, a mobile communication system has advanced from an analog one, as the first generation, through a digital one, as the second generation, to an asynchronous Wideband Code Division Multiple Access (WCDMA) or International Mobile Telecommunications-2000 (IMT-2000). As a result, the mobile communication system has a capability to provide global broadband roaming services at a rapid speed. The asynchronous WCDMA has various functions, for example one for wireless multi-media services, one for transmitting/receiving images which is either playing moving images/still images on a terminal in a Video On Demand (VOD) mode or photographing the images with a camera and then performing a bi-directional communication between users of the mobile communication using their own terminals.
This WCDMA terminal has an increasing importance to a part taking charge of an internal modem function as well as a part taking charge of applications including multimedia functions. Therefore, a terminal in which WCDMA is employed is exposed to an increased burden of Central Processing Unit (CPU) used to process a variety of multimedia data including still, as well as an increased amount of calculation data. Therefore, in order to make efficient use of WCDMA communication system, there is additional necessity not only for a modem, which provides a basic function for communication, but also for a module and memory, which take charge of applications allowing amount of calculations and errors of multimedia data to be decreased.
Existing techniques for encoding/decoding moving images based on MPEG-1, 2 and 4 or H.26×as well as still images based on JPEG and JPEG 2000 include a DCT/Inverse Discrete Cosine Transform (IDCT) algorithm, a DWT/Inverse Discrete Wavelet Transform (IDWT) algorithm and so on. The DCT/IDCT algorithm divides each image frame of moving images into a block of an 8×8 size, and then performs encoding/decoding in unit of this block. The DWT/IDWT algorithm divides each image into tiles of a proper size in the JPEG 2000 standard for still images, and then performs encoding/decoding in unit of each tile or relative to a certain area including a plurality of the tiles.
As mentioned above, in the case of the JPEG 2000 standard for still images, the DWT/IDWT algorithm performs tiling of appropriately dividing the corresponding still image into respective tiles and performs encoding/decoding of each tile. When encoding/decoding each image tile, the DWT/IDWT algorithm performs encoding/decoding relative to all image coefficients forming the tiles. When an encoded image is restored by this technique, the restored image has a high definition. However, since image coefficients corresponding to the whole tiles must each be calculated, there are problems in that an amount of calculation becomes increased, and in that a complexity of the image becomes increased. Further, in order to encode/decode images using this technique, demands for a memory capable of storing complicated images and calculated results and for enough time to calculate the complicated images are satisfied, which results in another problem.